This invention relates generally to lasers, and, more particularly to an autoalignment system for lasers in which the usual optical bench utilized for mounting the resonator reflectors is omitted.
Airborne electro-optical systems which require a high degree of pointing accuracy such as lasers, TV imagers, and cameras, are extremely sensitive to aircraft vibrations. Lasers utilize, for their operation, an active material located within a laser cavity which is made optically resonant by placing reflectors at either end thereof to form the optical resonator of the laser.
It has long been recognized that the alignment and optical figure of the resonator reflectors of the laser are of critical importance in order to maintain maximum output. Consequently, lasers subject to vibration such as in an aircraft are affected because of their requirement for precise alignment of the output beam. This not only means the overall device requires precise pointing control but that the alignment of the internal components such as the laser resonator reflectors or cavity mirrors is extrememly critical. Some factors which limit the pointing accuracy of high energy laser beams are as follows: dynamic alignment of the optical components, and vibration of mirrors, windows, optical benches and apertures. Such errors can be caused for example, by deformation of the optical bench itself on which the laser is mounted. Consequently, the relative motion of the optical resonator reflectors will reduce the output beam quality by adverse affect on resonator mode control. This relative motion can be quasi-steady (as due to G-loading) or vibratory in nature.
In the past, heavy rigid benches for mounting lasers thereon were passively suspended on soft springs which produced low resonant frequencies, and thereby attenuated the higher frequency aircraft vibration. These optical benches, however, weighed many thousands of pounds and therefore were too large and heavy for aircraft with strict weight volume limitations. Some aircraft also experienced severe vibration environment and high-g manuevers that made the precise alignment of the resonator reflectors even more difficult.
In addition, resonator reflector design is often specified to be within 1/10 or 1/20 of a wavelength of light and frequency to be within 1/100 of a wavelength of light. In other words, deviations may represent less than 1/1,000,000 of an inch. The heat flux at the optically reflective surface of a laser cavity mirror is typically within the range of 10 to 100 watts/cm.sup.2 or higher for many conventional lasers. Accordingly, cooling of the laser reflectors is required in order to maintain the stringent fabrication requirements of the reflectors under the high heat fluxes present at the optically reflective surface. The cooling of such laser reflectors also present a problem under conditions of severe vibrations or high-G maneuvers in that the coolant tubes must be manufactured in such a manner so as to be able to withstand severe vibration while maintaining optical alignment of the reflectors without the coolant fluid leaking from the tubes.
Therefore, a clearly defined need arises for an autoalignment system in the laser field, or any other field in which systems must be mounted which require a high degree of pointing accuracy and/or stability and yet is subject to a surrounding environment which is highly vibrational.